Distribution of the Primary Hereditary Characters 175 



in these organisms. But we find that in these, as in higher 

 animals, there are diverse packets of chemicals, which are 

 directly transmitted from parent to offspring, so that they 

 constitute the primary hereditary characters. In some of 

 the Protozoa these chromosomes are extremely minute and 

 numerous ; this is the case in the inf usorian Paramecium 

 caudatum (Figure 49). In others they are larger and 

 present in smaller numbers, appearing much as they do in 

 higher organisms (Figure 46). The primary hereditary 

 characters or chromosomes are shown for a number of 

 Protozoa in figures 46 to 50. 



In preparation for mating, and in mating itself, these 

 chromosomes undergo the same process of reduction in 

 number and recombination into new groups that occurs in 

 higher organisms. In figures 46 to 50 is shown what occurs 

 in some of the groups of Protozoa. 



Examine for example figure 46, which shows the process in 

 a protozoan belonging to the Gregarinidas, and parasitic in 

 the earthworm, as described by Mulsow (1911). The 

 chromosomal packets are in the form of eight long threads 

 (Figure 46, A) much resembling the chromosomes of many 

 higher animals. In ordinary multiplication by fission each 

 of these chromosomes splits lengthwise (Figure 46, B), and 

 half of each goes to each of the two offspring (C). In the 

 two parents before conjugation there are as usual eight of 

 these chromosomes, which become arranged side by side in 

 pairs, as occurs in higher organisms. This grouping into 

 four pairs is partly seen in figure 46, D and E. Now in 

 the early stages of mating, a division of the nucleus occurs 

 at which one member of each pair goes to one of the daughter 

 nuclei, one to the other (F, G, H). That is, each of the 

 two nuclei produced now receives four entire chromosomes, in 

 place of eight. Then in the mating, two such nuclei, each 



